1. Field of Invention
The present invention relates to microelectromechanical system (MEMS) microphone. More particularly, the present invention relates to the MEMS microphone with protection film from water, dust, et al.
2. Description of Related Art
MEMS chip, such as MEMS microphone, has a sensing diaphragm to sense the vibration of air pressure caused by acoustic signal, for example. The sensing diaphragm forms as a part of a sensing capacitor, so that the acoustic signal can be converted into electric signal.
FIG. 1 is a cross-sectional drawing, schematically illustrating a conventional MEMS chip. In FIG. 1, generally, a MEMS chip, such as a MEMS microphone, with diaphragm 58 is shown. The MEMS chip has a semiconductor substrate 40 and a dielectric structural layer 50 on the silicon substrate 40. The semiconductor substrate 40 has a cavity 44 and several venting holes 48 in the active region 46, which also serving a fixed electrode of a MEMS capacitor. The cavity 44 is connected with the chamber between the diaphragm 58 and the substrate 40 by the venting holes 48, so that the diaphragm can vibrates with the acoustic signal, which is usually received by the cavity 44. The dielectric structural layer 50 holds the diaphragm 58. The diaphragm 58 senses the acoustic signal. The other circuit part 54 is also formed in the dielectric structural layer 50. In fabrication, the dielectric structural layer 50 includes dielectric layer 52 and an etching stop layer 56 in multiple fabrication steps, to form the diaphragm 58 and the circuit part 54. The A person with ordinary skill in the art can understand how the MEMS structure is formed by the fabrication process in multiple steps.
Generally, the MEMS chip is divided into two parts of backplate and diaphragm. Referring to FIG. 1, the basic structure of the backplate includes the substrate 40 and the diaphragm is formed in the dielectric structural layer 50. In the following descriptions, the MEMS chip is then generally indicated by backplate and diaphragm as the two characteristic structures without showing the detail structure.
FIG. 2 is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. In FIG. 2, the MEMS chip 100 includes the backplate 102 and the diaphragm 104. The backplate 102 has a cavity 106 at one side to receive acoustic signal. The diaphragm 104 is disposed over the backplate 102 at a side opposite to the cavity. The backplate has a venting-hole layer 108 with multiple venting holes. A chamber is formed between the venting-hole layer 108 and the diaphragm 104, in which the space of the chamber is connected with the space of the cavity 106 by the venting holes. The MEMS chip 100 may be further implemented with a cap structure 110 as a MEMS microphone, in which the cap structure 110 can be formed over the diaphragm 104 by the adhesive layer 112, such as the glue layer. The cap structure 110 also has an auxiliary chamber 110a, so as to help the vibration of the diaphragm 104 in response to the acoustic signal received from the cavity 106.
FIG. 3 is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. In FIG. 3, another type of the conventional MEMS microphones in different structure may include a packaging board 120. A MEMS chip 100 and an application-specific integrated circuit (ASIC) 122 are disposed on the packaging board 120 and are electrically bounded by, for example, bonding wires or other bonding technology known in the art. Then a cap structure 114 on the packaging board 120 covers over the MEMS chip 100 and the ASIC 122. In order to receive the acoustic signal, the cap structure 114 has an acoustic port 116 to receive the acoustic signal. The auxiliary chamber 118 inside the cap structure 114 allows the diaphragm for more-easily vibrating with the acoustic signal.
FIG. 4 is a drawing of cross-sectional view, schematically illustrating a conventional MEMS chip. In FIG. 4, another type of the conventional MEMS microphones in different structure may include a packaging board 120. The packaging board 120 has an acoustic port 116. A MEMS chip 100 and an ASIC 122 are disposed on the packaging board 120 and are electrically bounded by, for example, bonding wires. However, the cavity of the MEMS chip 100 is matched to the acoustic port 116 of the packaging board 120, so the cavity can receive the acoustic signal. A cap structure 114 on the packaging board 120 covers over the MEMS chip 100 and the ASIC 122. In this situation, the cap structure 114 may need not the acoustic port. The auxiliary chamber 118 inside the cap structure 114 allows the diaphragm for more-easily vibrating with the acoustic signal.
The conventional MEMS chip can be designed in various manners, but not limited to the types described above. It should be noted that the vibration amplitude of the diaphragm would determine the sensitivity. However, the conventional MEMS chip during the subsequent fabrication processes, such as the process to packaging in circuit board, may receive intruding material between the diaphragm and the venting-hole layer and then reduce the performance of the diaphragm.